Abstract Our project goal is to investigate a new, minimally-invasive regenerative nanotherapy for small (<5.5 cm diameter) abdominal aortic aneurysms (AAAs). AAAs are rupture-prone expansions of the abdominal aorta, which primarily afflict the elderly. Surgery on small AAAs provides no therapeutic benefit and does not justify the inherent risk and complications. Restoring extracellular matrix (ECM) homeostasis in the AAA wall is critical to be able to regress AAA growth, but is challenged by a) chronic breakdown of elastic and collagen fibers in the aorta wall by matrix metalloproteases (MMPs) and b) inherently poor auto-regenerative repair of the elastic fibers by adult vascular smooth muscle cells (SMCs), which is difficult to overcome3,4. We have recently developed novel, polylactic-co- glycolic acid (PLGA) nanoparticles (NPs) for sustained, steady-state release of doxycycline, an MMP inhibitor, in AAA tissue following one-time, catheterwise intra-aortal delivery. This mode of delivery, avoids the systemic, and elastin biosynthesis-inhibitoryeffects of oral DOX therapy, and enables sustained, steady DOX release at doses < 10 ?g/ml which we have found to both inhibit MMPs and stimulate elastogenesis. Our NPs also uniquely provide pro-elastin regenerative & anti-MMP properties, separate from that of released DOX, and are attributed to positive charge & hydrophobic groups due to cationic amphiphiles we incorporated on the NP surface. In this project, we will broadly clarify the signaling mechanisms underlying the pro-regenerative and anti-MMP effects of DOX at sub-therapeutic doses, optimize their formulations for significant functional benefit, develop modalities for efficient delivery to AAA tissues, and demonstrate therapeutic efficacy in regressing formed AAAs in an animal model. Our specific aims (SAs) will test hypotheses that a) pro-matrix regenerative effects of DOX represent downstream effects of its inhibition of the JNK pathway, and subsequent upregulation of transforming growth factor-?1 (TGF-?1), b) inhibiting JNK with DOX will provide synergy of action over other JNK inhibitors by additionally engaging other, more direct mechanisms of MMP inhibition, and c) the regenerative stimulus provided by sustained low-level DOX release from our pro-regenerative NPs will restore ECM homeostasis in the AAA wall to regress its growth. SA1 will investigate DOX dose-specific inhibition of JNK & downstream effects on de novo elastic matrix assembly and anti-proteolytic activity in rat AAA SMC cultures. SA2 will identify DOX-NP formulations that significantly augment de novo elastic matrix assembly and matrix repair in matrix-disrupted rat AAA SMC cultures. SA3 will develop magnetic targeting modalities for DOX-NP delivery to the AAA wall. SA4 will assess therapeutic efficacy of magnetically-responsive DOX-NPs in a rat AAA model. This study will establish feasibility of a new, minimally-invasive matrix regenerative therapy to regress small AAAs, which can potentially reduce or delay need for future surgical intervention in high risk AAA patients. Our study will justify further validation in larger animal models towards rationalizing clinical trials.